A standard refrigeration or HVAC system includes a refrigerant fluid, an evaporator, a compressor, a condenser, and an expansion valve. In a typical refrigeration cycle, the refrigerant fluid begins in a liquid state under low pressure. The evaporator evaporates the low pressure liquid, and the liquid becomes a low pressure vapor. The compressor draws the vapor in and compresses it, producing a high pressure vapor. The compressor then passes the high pressure vapor to the condenser. The condenser condenses the high pressure vapor, generating a high pressure liquid. The cycle is completed when the expansion valve expands the high pressure liquid, resulting in a low pressure liquid. By means of example only, the refrigerant fluid may include the any suitable refrigerant including, but not limited to R-410A, R-407C, ammonia, or ethyl chloride.
A primary component in HVAC systems is a positive displacement compressor, which receives a cool, low pressure gas and by virtue of a compression device that may include one or more compression members, exhausts a hot, high pressure gas. One type of positive displacement compressor is a screw compressor, which generally includes two cylindrical rotor compression members mounted on separate shafts inside a hollow, double-barreled casing. The side-walls of the compressor casing typically form two parallel, overlapping cylinders which house the rotors side-by-side, with their shafts parallel to the ground. Screw compressor rotors typically have helically extending lobes and grooves on their outer surfaces forming a large thread on the circumference of the rotor, also referred to as an involute surface. During operation, the threads of the rotors mesh together, with the lobes on one rotor meshing with the corresponding grooves on the other rotor to form a series of gaps between the rotors. These gaps form a continuous compression chamber that communicates with the compressor inlet opening, or “port,” at one end of the casing, continuously reduces in volume as the rotors turn to compress the gas, and exhausts the compressed gas at a discharge port at the opposite end of the casing for use in the system.
The screw compressor creates a significant amount of noise. To mediate the noise produced by the compressor, a muffler may be installed on the discharge of the compressor. One type of muffler utilizes a baffle inside the muffler body to reduce noise. The baffle includes a surface substantially perpendicular to the flow of fluid. The fluid entering the muffler is reflected off the baffle. The reflection of fluid off the baffle attenuates the noise created by the compressor. This type of muffler may be attached at or near the discharge of the compressor to provide noise attenuation for the compressor system.
In operation, the compressor works the fluid to achieve a high pressure at the discharge. However, when the compressor is no longer operating, the fluid present in the HVAC refrigerant loop on the high pressure side of the compressor (i.e., the side of the compressor toward the condenser in the HVAC loop) flows in a direction toward the low pressure side of the compressor (i.e., the side of the compressor toward the evaporator in the HVAC loop) until a state of equilibrium between the formerly high and formerly low pressure sides is achieved. Thus, the high pressure side equalizes with the low pressure side when the compressor stops operating. However, during the time in which the fluid is equalizing, the fluid flows through the compressor and over the compression members in a direction that is opposite the direction that the fluid flows during compressor operation. For example, in a screw compressor, when the fluid rushes to the low pressure side of the compressor, the fluid passes over the rotors of the screw compressor. This backflow of fluid causes the rotors to spin in the opposite direction of normal operation at a high rate of speed creating an undesirable sound level and frequency.
What is needed is a device and/or method that substantially prevents the rush of fluid from the high pressure side to the low pressure side when the compressor stops operating and/or reduces the amount of noise created when the compressor is deactivated.